When a control device with a learning function and a motor control device are in operation, a controlled object sometimes produces a periodicity disturbance.
In case of for example an electric motor as the controlled object that produces the periodicity disturbance, a pulsation called as torque ripple is produced, which causes various problems, such as vibration, noises, poor riding comfort, resonance of machines etc. Particularly, in widely used magnet embedded type synchronous motors (which will be called PM motor hereinafter), cogging torque ripple and reluctance torque ripple are complicatedly produced. For suppressing the production, various methods for suppressing the torque ripple by electrically applying compensation signals to a controlled object to cancel pulsation have been known.
The methods can be roughly grouped into two, one being a feedforward compensation method that compensates the torque ripple based on an approximate expression and an analytical result of electromagnetic field and the other being a feedback method.
The feedback method is grouped into a method in which learning is carried out through a torque meter, a method in which suppression control is carried out by estimating a torque ripple from a motor current ripple and a torque ripple disturbance observer method in which suppression control is carried out based on current value and rotation speed value detected. Although these feedback methods can handle a ripple characteristic fluctuation online, these methods have an approximation error that is inevitably produced when the torque ripple is estimated from the current ripple and a limitation on frequency band that is exhibited by a disturbance observer filter when working in a high frequency band.
The torque ripple is a periodicity disturbance produced by a rotational fluctuation degree of the motor, and a higher order component of the periodicity disturbance tends to match with a machine resonance frequency even when the motor runs at a lower speed. Accordingly, in case of applying a learning control to a variable speed drive system of oscillatory type, it is necessary to consider counter-measures against unstable phenomena caused by sudden changes in amplitude and phase reversal. For achieving this, it is generally necessary to ask the assistance of a complicated high order model and a suitable control/adjustment of the model, and thus, effective control of the periodicity disturbance like the torque ripple is difficult. Measures for suppressing such periodicity disturbance are known from Patent Document-1.
In the measures of Patent Document-1, as is seen from FIG. 18, a torque command Tref is inputted to a command value converting portion 1 to produce current commands id* and iq* of d and q axes of a rotating coordinate system (mutually perpendicular dq axes) that is synchronized with rotation of the electric motor, and the current commands are inputted to an inverter 2 (vector controlling device) to be subjected to a vector controlling. Based on the current commands id* and iq*, the inverter 2 produces an output to control a PM motor 3 to which a load is connected through a shaft. A shaft torque detected value Tdet detected by a torque detecting device mounted to the shaft and a rotor phase angle θ detected by a position detecting device mounted to the shaft are inputted into an observer portion 4.
In the observer portion 4, a periodic pulsation of the PM motor 3 is detected as a direct current by a frequency component extraction means of Fourier transforming (Fourier transform portion FT), and a periodicity disturbance on the frequency component is estimated by a periodicity disturbance observer compensating portion 4a, and the estimated value is added to the current command iq* in a manner to suppress the periodicity disturbance.
Denoted by SC in FIG. 18 is n-order (or dimensional) sinusoidal/cosine wave generating portion, and Tr denotes a converting period and n denotes a compensating order (or degree).
The periodicity disturbance observer compensating portion 4a serves as one of control means suppressing a periodicity disturbance, and a basic construction of the compensating portion 4a is the same as that of a conventional disturbance observer, and the portion 4a controls disturbance components separately. By using a system identification model, which exhibits a complex vector for each frequency component, as a reversed system model of the disturbance observer, the disturbance of the frequency to be controlled is directly estimated and compensated. With this, a high control effect can be obtained against an intended frequency irrespective of the order, even though the controlling construction is relatively simple in construction.